JP2020102539A - Piezoelectric composition and piezoelectric element - Google Patents

Abstract

To provide a piezoelectric composition having a high electric resistivity and a large piezoelectric constant.SOLUTION: A piezoelectric composition includes an oxide containing bismuth, barium, iron, and titanium, and silver. The oxide has a perovskite structure. The mass of oxide is represented as MABO3, and the mass of silver is represented as MAG. 100×MAG/MABO3 is 0.01 or more and 10.00 or less.SELECTED DRAWING: Figure 1

Description

The present invention relates to a piezoelectric composition and a piezoelectric element.

Most of the piezoelectric compositions currently put into practical use are solid solutions (so-called PZT-based piezoelectric compositions) made of lead zirconate (PbZrO ₃ ) and lead titanate (PbTiO ₃ ). The PZT-based piezoelectric composition contains a large amount of lead oxide (PbO) as a main component. Since lead oxide is extremely volatile even at low temperatures, a large amount of lead oxide will diffuse into the atmosphere during the manufacturing process of the piezoelectric composition or the piezoelectric element using the same. Since lead is an environmental pollutant that harms the human body, there is a need for a piezoelectric composition that does not contain lead.

A typical lead-free piezoelectric composition is bismuth ferrate (BiFeO ₃ ). For example, the following Patent Document 1 and Non-Patent Document 1 describe a solid solution (BFO-BTO piezoelectric composition) composed of BiFeO ₃ and barium titanate (BaTiO ₃ ). However, since the conventional BFO-BTO piezoelectric composition has a low electric resistivity and a leak current is easily generated in the BFO-BTO piezoelectric composition, the conventional BFO-BTO piezoelectric composition does not always have sufficient piezoelectricity. I haven't. For example, the piezoelectric constant d ₃₃ of the BFO-BTO piezoelectric composition after the polarization treatment is about 135 pC/N. The following Patent Document 2 discloses a method for producing a dielectric ceramic from a powder containing BiFeO ₃ , Bi ₂ Fe ₄ O ₉ and Bi ₂₅ FeO ₃₉ . According to this manufacturing method, the leak current in the dielectric ceramics (piezoelectric composition) is reduced. However, Patent Document 2 below does not report a specific piezoelectric constant of the dielectric ceramics.

JP-A-2009-298621 Japanese Patent No. 6146453

Wei et. al, Dielectric, Ferroelectric, and Piezoelectric Properties of BiFeO3-BaTiO3 Ceramics, J. Am. Am. Ceram. Soc. , 96 [10] (2013) 3163-3168.

An object of the present invention is to provide a piezoelectric composition having a high electric resistivity and a large piezoelectric constant, and a piezoelectric element including the piezoelectric composition.

A piezoelectric composition according to one aspect of the present invention includes an oxide containing bismuth, barium, iron, and titanium, and silver, the oxide has a perovskite structure, and the mass of the oxide is _MABO3 . It is represented, the mass of silver is represented as M _AG, and 100×M _AG /M _ABO3 is 0.01 or more and 10.00 or less.

The piezoelectric composition according to one aspect of the present invention may further include at least one element D selected from the group consisting of vanadium, niobium, tantalum, molybdenum, tungsten, and manganese.

The piezoelectric composition according to one aspect of the present invention may further contain at least niobium as the element D.

The total mass value of the element D may be represented as M _D, and 100×M _D /M _ABO3 may be 0.00 or more and 5.00 or less.

At least a portion of the _oxide, x _[Bi m FeO 3] may be expressed as _{-y [Ba n TiO 3],} x is may be 0.6 to 0.8, y is 0 .2 or more and 0.4 or less, x+y may be 1, m may be 0.96 or more and 1.06 or less, and n is 0.96 or more and 1.06 or less. You can

A piezoelectric element according to one aspect of the present invention includes the above piezoelectric composition.

According to the present invention, there are provided a piezoelectric composition having a high electric resistivity and a large piezoelectric constant, and a piezoelectric element including the piezoelectric composition.

FIG. 1 is a perspective view of a unit cell of an oxide perovskite structure included in a piezoelectric composition according to an embodiment of the present invention. FIG. 2 is a schematic perspective view of the piezoelectric element according to the embodiment of the present invention.

Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings. The present invention is not limited to the embodiments described below.

The piezoelectric composition according to this embodiment includes an oxide containing bismuth (Bi), barium (Ba), iron (Fe), and titanium (Ti), and silver (Ag). For convenience of description, the oxide containing Bi, Ba, Fe and Ti is referred to as “BFO-BTO”. BFO-BTO has a perovskite structure. BFO-BTO is at least one crystal selected from the group consisting of tetragonal crystals having a perovskite structure, cubic crystals having a perovskite structure, and rhombohedral crystals having a perovskite structure. .. An example of a unit cell having a perovskite structure is shown in FIG. The unit cell uc may be composed of the element A located at the A site, the element B located at the B site, and oxygen (O). Element A may be Bi or Ba. The element B may be Fe or Ti.

The mass of oxide (BFO-BTO) is denoted as _MABO3 . The mass of Ag is expressed as M _AG . The M _AG, translates into a single mass of Ag. 100×M _AG /M _ABO3 is 0.01 or more and 10.00 or less. When 100×M _AG / _MABO3 is 0.01 or more and 10.00 or less, the piezoelectric composition can have a high electrical resistivity (ρ) and a large piezoelectric constant (d ₃₃ ). The reason is as follows.

A part of oxygen that constitutes the perovskite structure of BFO-BTO is easily lost. That is, in the perovskite structure, oxygen vacancies are likely to occur. The lack of some oxygen constituting the perovskite structure is represented by the following formula 1, for example. Two electrons (e ⁻ ) are generated in association with the generation of one oxygen vacancy (V _O ^″ ). Therefore, when the piezoelectric composition contains oxygen vacancies, a leak current due to the oxygen vacancies is likely to occur in the piezoelectric composition. In other words, the piezoelectric composition containing oxygen vacancies has a low electric resistivity. As a result, it is difficult to apply a high voltage to the piezoelectric composition, the piezoelectric composition is not sufficiently polarized, and it is difficult for the piezoelectric composition to have a large piezoelectric constant. However, since the piezoelectric composition according to the present embodiment contains Ag, a part of Ba located at the A site of the perovskite structure of BFO-BTO is replaced with Ag. The substitution of Ba with Ag is represented by the following formula 2, for example. Ag _{BA in} Formula 2 is Ag located at the A site of the perovskite structure instead of Ba. Since the valence of Ba forming the perovskite structure is 2, and the valence of Ag is 1, holes (h ⁺ ) are generated along with the substitution of Ba with Ag. When 100×M _AG /M _ABO3 is 0.01 or more and 10.00 or less, electrons due to oxygen vacancies and holes due to Ag are easily balanced. That is, Ag functions as an electron acceptor. As a result, the electric resistivity of the piezoelectric composition is higher than that of the piezoelectric composition having 100×M _AG / _MAB03 outside the above range, and the leak current in the piezoelectric composition is suppressed. Therefore, it is possible to apply a high voltage to the piezoelectric composition, the piezoelectric composition is sufficiently polarized, and the piezoelectric composition can have a large piezoelectric constant. For example, when 100×M _AG / _MABO3 is within the above range, the piezoelectric composition can have ad ₃₃ of 140 pC/N or more. When 100×M _AG /M _ABO3 is less than 0.01, it is difficult to sufficiently offset the electrons due to oxygen vacancies by the holes due to Ag. Even when 100×M _AG /M _ABO3 is 0.01 or more and more than 10.00, it is difficult to balance the charges in the piezoelectric composition, and the crystal structure (perovskite structure) of BFO-BTO is easily damaged by excessive Ag, The piezoelectric constant of the piezoelectric composition tends to decrease. Since the piezoelectric composition _tends to have a high electric resistivity and a large piezoelectric constant, 100×M _AG / _MAB03 is preferably 0.01 or more and 5.00 or less, more preferably 0.01 or more and 0.50 or less. It may be the following. If the piezoelectric composition does not contain Ag but contains copper (Cu) having a valence of 2, it is difficult for the piezoelectric composition to have a high electric resistivity, and it is also difficult for it to have a large piezoelectric constant. .. However, the piezoelectric composition may contain Cu in addition to Ag. The voltage applied to the piezoelectric composition may be paraphrased as an electric field.
O→V _O ^″ +2e ⁻ (1)
Ag → Ag _BA +h ⁺ (2)

The piezoelectric composition may further include at least one element D selected from the group consisting of vanadium (V), niobium (Nb), tantalum (Ta), molybdenum (Mo), tungsten (W), and manganese (Mn). .. The piezoelectric composition may include multiple types of element D. The valence of the element D is 5 or 6. For example, vanadium, niobium, and tantalum each have a valence of 5. The valence of each of molybdenum, tungsten and manganese is 6. When the piezoelectric composition contains at least one element D, the electrical resistivity (ρ) of the piezoelectric composition is likely to increase, and the piezoelectric constant (d ₃₃ ) of the piezoelectric composition is likely to increase. The reason is as follows. However, even if the piezoelectric composition does not contain the element D, it is possible that the piezoelectric composition has a high electric resistivity and a large piezoelectric constant because the piezoelectric composition contains Ag.

Since Bi easily volatilizes, there is a possibility that a part of Bi located at the A site of the perovskite structure will be lost during the manufacturing process of the piezoelectric composition. That is, in the perovskite structure, Bi vacancies may occur. The lack of some Bi constituting the perovskite structure is represented by, for example, Equation 3 below. Since the valence of Bi constituting the perovskite structure is 3, three holes (h ⁺ ) are generated along with the generation of one Bi vacancy (V _BI ^″″ ). Therefore, when the piezoelectric composition includes Bi holes, a leak current due to holes is likely to occur in the piezoelectric composition. In other words, since the piezoelectric composition contains the holes of Bi, the electric resistivity of the piezoelectric composition is likely to decrease. As a result, it is difficult to apply a high voltage to the piezoelectric composition, it is difficult to sufficiently polarize the piezoelectric composition, and it is difficult to increase the piezoelectric constant of the piezoelectric composition. The valence of Fe ions forming the perovskite structure of BFO-BTO is 3. However, the valence of Fe ions may decrease during the manufacturing process of the piezoelectric composition. The decrease in the valence of Fe ions is expressed by the following formula 4, for example. Since the valence of Fe constituting the perovskite structure is 3, one hole (h ⁺ ) is generated as the valence of Fe decreases. Therefore, as the valence of Fe decreases, a leak current due to holes easily occurs in the piezoelectric composition. In other words, as the valence of Fe decreases, the electrical resistivity of the piezoelectric composition tends to decrease. As a result, it is difficult to apply a high voltage to the piezoelectric composition, it is difficult to sufficiently polarize the piezoelectric composition, and it is difficult to increase the piezoelectric constant of the piezoelectric composition. On the other hand, when the piezoelectric composition contains the element D, a part of the element located at the B site of the perovskite structure of BFO-BTO is replaced with the element D. The element located at the B site is, for example, Ti. When the valence of the element D is 5, the substitution of Ti by the element D is represented by the following formula 5, for example. When the valence of the ion of the element D is 6, the substitution of Ti by the element D is represented by the following formula 6, for example. D _TI in Formulas 4 and 5 is an element D located at the B site of the perovskite structure instead of Ti. Since the valence of Ti constituting the perovskite structure is 4, and the valence of the element D is 5 or 6, an electron (e ⁻ ) is generated with the replacement of Ti with the element D. Therefore, holes due to the vacancies of Bi, holes due to the decrease in the valence of Fe, and electrons due to the element D are easily balanced. That is, the element D functions as an electron donor. As a result, the electric resistivity of the piezoelectric composition is likely to be higher than that of the piezoelectric composition not containing the element D, and the leak current in the piezoelectric composition is easily suppressed. Therefore, a high voltage is easily applied to the piezoelectric composition, the piezoelectric composition is easily polarized, and the piezoelectric composition is likely to have a large piezoelectric constant.
Bi→V _BI ^''' +3h ⁺ (3)
Fe ³⁺ →Fe ²⁺ +h ⁺ (4)
^{_{D → D TI + e - (}} 5)
D→D _TI +2e ⁻ (6)

The piezoelectric composition may further contain at least niobium as the element D. The piezoelectric composition containing niobium tends to have a high electric resistivity as compared with the piezoelectric composition containing the element D other than niobium. Therefore, the piezoelectric composition containing niobium tends to have a larger piezoelectric constant than the piezoelectric composition containing the element D other than niobium.

The total mass value of the element D may be expressed as M _D, and 100×M _D /M _ABO3 may be 0.00 or more and 5.00 or less. M _D may be paraphrased as the total value of the mass of the element D alone. Since 100×M _D /M _ABO3 is 0.00 or more and 5.00 or less, the holes are derived from the holes of Bi, the holes are derived from the decrease of the valence of Fe, and the element D is derived. The electrons are easy to balance. As a result, the electric resistivity of the piezoelectric composition is _likely to increase as compared with the electric resistivity of the piezoelectric composition in which 100×M _D /M _ABO3 is out of the above range, and the leak current in the piezoelectric composition is easily suppressed. Therefore, a high voltage is easily applied to the piezoelectric composition, the piezoelectric composition is easily polarized, and the piezoelectric composition is likely to have a large piezoelectric constant. For example, when 100×M _D /M _ABO3 is within the above range, the piezoelectric composition can have d ₃₃ of 150 pC/N or more. Since the piezoelectric composition is likely to have a high electrical resistivity and a large piezoelectric constant, 100×M _D /M _ABO3 is preferably 0.01 or more and 1.00 or less, more preferably 0.01 or more and 0.10 or less. It may be.

The reason why the piezoelectric composition has a high electric resistivity and a large piezoelectric constant is not necessarily limited to the above mechanism.

At least some of the oxides (BFO-BTO) may be represented by the following chemical formula A. The following chemical formula A is equal to the chemical formula B.
_{x [Bi m FeO 3] -y} [Ba n TiO 3] (A)
_{(Bi xm Ba yn) (Fe} x Ti y) O 3 (B)
x+y is 1. x may be 0.6 or more and 0.9 or less, or 0.6 or more and 0.8 or less. y may be 0.1 or more and 0.4 or less, or 0.2 or more and 0.4 or less. m may be 0.96 or more and 1.06 or less. n may be 0.96 or more and 1.06 or less. When x is 0.6 or more and 0.8 or less and y is 0.2 or more and 0.4 or less, the electric composition tends to have a high electric resistivity and a large piezoelectric constant.

The above _{M ABO3,} based on the assumption that constitute the only _{oxides Bi} contained in the piezoelectric composition, Fe, all elements of Ba and Ti is represented by Chemical Formula _{A, x [Bi m FeO 3} ] - It is a calculated value of the mass of y[Ba _n TiO ₃ ]. That is, M _ABO3 is a calculated value for defining 100×M _AG /M _ABO3 . In practice, some Ba or Bi in formula A or formula B may be replaced by Ag. Part of Ti or Fe in the chemical formula A or the chemical formula B may be replaced with the element D. That is, the oxide containing Bi, Ba, Fe and Ti may further contain Ag. The oxide containing Bi, Ba, Fe and Ti may further contain both Ag and the element D. The piezoelectric composition may consist of only one oxide consisting of Bi 2 _, Fe, Ba, Ti, Ag and O 2. The piezoelectric composition may be composed of only one kind of oxide consisting of Bi _, Fe, Ba, Ti, Ag, and elements D and O. A part of the piezoelectric composition may be a phase composed of Bi _m FeO ₃ . Some of the piezoelectric _composition, may be a phase consisting Ba n TiO _3. The piezoelectric composition may contain elements other than Bi _, Fe, Ba, Ti, Ag, and elements D and O as impurities or additives. For example, the piezoelectric composition includes sodium (Na), potassium (K), magnesium (Mg), aluminum (Al), sulfur (S), zirconium (Zr), silicon (Si), phosphorus (P), copper (Cu). ), zinc (Zn), and hafnium (Hf). The piezoelectric composition according to the present embodiment may not contain Pb. However, the piezoelectric composition containing Pb is not necessarily excluded from the technical scope of the present embodiment.

The average composition of the entire piezoelectric composition may be analyzed by, for example, X-ray fluorescence analysis (XRF method) or inductively coupled plasma (ICP) emission spectroscopy. The structure of the piezoelectric composition may be identified by X-ray diffraction (XRD) method.

As shown in FIG. 2, the piezoelectric element 10 according to the present embodiment includes a substrate 2, a first electrode 4 overlapping the surface of the substrate 2, a piezoelectric body 6 overlapping the surface of the first electrode 4, and a piezoelectric body 6. The second electrode 8 overlapping the surface of the. The piezoelectric body 6 includes the piezoelectric composition according to this embodiment. The piezoelectric body 6 may be a sintered body of a piezoelectric composition. The piezoelectric body 6 may include other components in addition to the piezoelectric composition. The piezoelectric body 6 shown in FIG. 2 is a thin rectangular parallelepiped, but the shape and dimensions of the piezoelectric body 6 are not limited. The substrate 2 may be, for example, metal, semiconductor, resin, glass or ceramics. The composition of each of the first electrode 4 and the second electrode 8 is not limited as long as the first electrode 4 and the second electrode 8 have conductivity. Each of the first electrode 4 and the second electrode 8 may be a simple metal or an alloy. Each of the first electrode 4 and the second electrode 8 may be a metal oxide having conductivity.

The piezoelectric element according to the present embodiment has various uses. The piezoelectric element may be, for example, a piezoelectric microphone, a piezoelectric transformer, a harvester, an oscillator, a resonator, or an acoustic multilayer film. The piezoelectric element may be, for example, a piezoelectric actuator. Piezoelectric actuators may be used in haptics. That is, the piezoelectric actuator may be used for various devices that require feedback by skin sensation (tactile sensation). The device for which feedback by skin sense is required may be, for example, a wearable device, a touch pad, a display, or a game controller. Piezoelectric actuators may be used in head assemblies, head stack assemblies, or hard disk drives. The piezoelectric actuator may be used, for example, in a printer head or an inkjet printer device. Piezoelectric actuators may be used in piezoelectric switches. The piezoelectric element may be, for example, a piezoelectric sensor. The piezoelectric sensor may be used in, for example, a gyro sensor, a pressure sensor, a pulse wave sensor, an ultrasonic sensor, or a shock sensor. Each of the piezoelectric elements described above may be a part or all of the MEMS.

The piezoelectric composition according to this embodiment may be manufactured by the following manufacturing method.

In manufacturing a piezoelectric composition, raw material powder (raw material particles) is prepared from a starting raw material. A compact is formed by press-molding the raw material particles. A sintered body is obtained by firing the molded body. The piezoelectric body is obtained by subjecting the sintered body to polarization treatment. The piezoelectric composition according to the present embodiment means both a sintered body before polarization treatment and a sintered body after polarization treatment. The details of each step are as follows.

In the granulation step, the starting material for the piezoelectric composition is weighed. Multiple types of starting materials may be used. The starting material comprises Bi _, Fe, Ba, Ti and Ag. The starting material may further contain the element D. The starting material may be a simple substance (metal) of each element or a compound. The compound may be, for example, an oxide, carbonate, hydroxide, oxalate, nitrate or the like. Each starting material may be solid (eg powder). By weighing each starting material, the molar ratio of Bi, Fe, Ba and Ti in the whole starting material may be adjusted to the molar ratio of Bi, Fe, Ba and Ti in the above chemical formula A. The mass of Ag in the entire starting material may be adjusted so that 100×M _AG / _MABO3 is 0.01 or more and 10.00 or less. The total value of the mass of the element D in the entire starting material may be adjusted so that 100×M _D /M _ABO3 is 0.00 or more and 5.00 or less.

The bismuth compound (Bi compound) may be bismuth oxide (Bi ₂ O ₃ ), bismuth nitrate (Bi or (NO ₃ ) ₃ ), and the like. The iron compound (Fe compound) may be iron oxide (Fe ₂ O ₃ ), iron chloride (FeCl ₃ ), iron nitrate (Fe(NO ₃ ) ₃ ), or the like. The barium compound (Ba compound) includes barium oxide (BaO), barium carbonate (BaCO ₃ ), barium oxalate (C ₂ BaO ₄ ), barium acetate ((CH ₃ COO) ₂ Ba), barium nitrate (BaSO ₄ ), Alternatively, it may be barium titanate (BaTiO ₃ ). The titanium compound (Ti compound) may be titanium oxide (TiO ₂ ). The Ag compound may be Ag ₂ O (silver oxide). The compound of element D may be an oxide of element D. Examples of the oxide of the element D include vanadium oxide (V ₂ O ₅ ), niobium oxide (Nb ₂ O ₅ ), tantalum oxide (Ta ₂ O ₅ ), molybdenum oxide (MoO ₃ ), tungsten oxide (WO ₃ ), and It may be at least one selected from the group consisting of manganese oxide (MnO ₃ ).

In the granulation step, raw material particles are prepared from the above-mentioned starting materials. Plural kinds of raw material particles having different compositions may be prepared. The method for preparing the raw material particles may be as follows, for example.

The slurry may be prepared by mixing the starting materials and the solvent. The starting materials in the slurry may be pulverized by wet mixing the slurry using a ball mill or the like. The solvent used to prepare the slurry may be, for example, water. The solvent may be an alcohol such as ethanol. The solvent may be a mixture of water and ethanol. The starting materials after the wet mixing may be dried by a spray dryer or the like.

A temporary molded body is formed by molding the crushed mixture of starting materials. A temporary sintered body is obtained by heating the temporary molded body in an oxidizing atmosphere. The oxidative atmosphere may be, for example, the atmosphere. The calcination temperature may be 700° C. or higher and 1050° C. or lower. The calcination time may be about 1 to 3 hours. Raw material particles are obtained by crushing the pre-sintered body. A slurry may be prepared by mixing the raw material particles and a solvent. The raw material particles in the slurry may be pulverized by wet mixing the slurry using a ball mill or the like. The average value of the primary particle diameter of the raw material particles may be adjusted by this wet mixing. The average primary particle diameter of the raw material particles may be, for example, 0.01 μm or more and 20 μm or less. The raw material particles after wet mixing may be dried by a spray dryer or the like.

A molded body is obtained by press molding a mixture of raw material particles and a binder. The binder may be an organic binder such as polyvinyl alcohol or ethyl cellulose. A dispersant may be added to the binder.

A sintered body is obtained by sintering the molded body in an oxidizing atmosphere. Before the firing of the molded body, the binder removal treatment of the molded body may be performed. That is, the binder in the molded body may be decomposed by heating the molded body. The binder removal treatment and the firing may be continuously performed. The debinding process and the firing may be performed separately. The firing temperature may be 900° C. or higher and 1250° C. or lower. The firing time may be 1 hour or more and 8 hours or less.

Prior to the polarization treatment described below, a thin plate made of a sintered body may be formed by cutting the sintered body. Lapping may be performed on the surface of the thin plate of the sintered body. A cutter such as a cutter, a slicer or a dicing saw may be used to cut the sintered body. After lapping, temporary electrodes for polarization treatment are formed on each of a pair of opposing surfaces of the sintered body. The temporary electrode may be formed by vacuum vapor deposition or sputtering. The temporary electrode is easily removed by an etching process using a ferric chloride solution or the like.

In the polarization process, a polarization electric field is applied between a pair of temporary electrodes that sandwich the sintered body. In the polarization process, the sintered body may be heated. The temperature of the sintered body in the polarization treatment may be 80° C. or higher and 300° C. or lower. The time for which the polarization electric field is applied may be 1 minute or more and 30 minutes or less. The polarization electric field may be 0.9 times or more the coercive electric field of the sintered body.

After the polarization treatment, the temporary electrode is removed from the sintered body. By processing the sintered body, a piezoelectric composition (piezoelectric body) having a desired shape may be formed.

Although the preferred embodiment of the present invention has been described above, the present invention is not necessarily limited to the above-described embodiment. For example, the piezoelectric composition according to the present invention may be a piezoelectric thin film.

Hereinafter, the present invention will be described in detail with reference to Examples and Comparative Examples. However, the present invention is not limited to the following examples.

(Example 1)
Bi ₂ O ₃ powder, Fe ₂ O ₃ powder, BaCO ₃ powder, TiO ₂ powder, and Ag (metal simple substance) powder were used as starting materials. The molar ratio of Bi, Fe, Ba, and Ti in the entire starting material is adjusted so that the molar ratio of Bi, Fe, Ba, and Ti in the following chemical formula A1 matches BaCO ₃ , TiO ₂ , Bi ₂ O _3, and Fe ₂ O ₃ were weighed. In the case of Example 1, the values of x and y in the chemical formula A1 were the values shown in Table 1 below. Ag was weighed such that 100×M _AG /M _ABO3 was 5.2. M _AG is the mass of Ag contained in the starting material. M _ABO3 is x[BiFeO ₃ ]-y[BaTiO ₃ based on the assumption that all the elements of Bi _, Fe, Ba and Ti contained in the starting material constitute only the oxide represented by the following chemical formula A1. ] Is the calculated value of the mass. In the following, 100×M _AG /M _ABO3 is expressed as α.
x[BiFeO ₃ ]-y[BaTiO ₃ ] (A1)

All starting materials and pure water were mixed in a ball mill for 10 hours. After the mixed starting material was dried, the starting material was press-molded to obtain a temporary molded body. A temporary fired body was obtained by heating the temporary formed body at 800°C. The calcined body was crushed with a ball mill. Raw material particles were obtained by drying the crushed temporary sintered body. A molded body was obtained by press molding a mixture of raw material particles and a binder (polyvinyl alcohol). The binder was removed by heating the molded body. After the binder removal treatment, the molded body was fired in the atmosphere of 1000° C. for 4 hours to obtain a sintered body. The sintered body corresponds to the piezoelectric composition before polarization treatment.

By processing the sintered body using a double-sided lapping machine and a dicing saw, a plate made of the sintered body was formed. The dimension of the sintered body after processing was 16 mm in length×16 mm in width×0.5 mm in thickness.

Electrodes made of Ag were formed on both sides of the sintered body using a vacuum vapor deposition apparatus. The thickness of each electrode was 1.5 μm. The size of each electrode was 15 mm×15 mm.

By applying a DC electric field to the piezoelectric composition sandwiched between the pair of electrodes, the electrical resistivity ρ (unit: Ω·cm) of the piezoelectric composition was measured. The DC electric field was 0.1 kV/cm. The time for which the DC electric field was applied to the piezoelectric composition was 40 seconds. Ρ of Example 1 is shown in Table 1.

The sintered body was polarized by applying an electric field to the sintered body sandwiched by the pair of electrodes. The strength of the electric field applied to the sintered body was 1.5 to 2 times the coercive electric field. The electric field was applied to the sintered body for 15 minutes. The above polarization treatment was carried out in a silicon oil bath having a temperature of 120°C. After the polarization treatment, the electrical resistivity ρ of the piezoelectric composition was measured again. The electrical resistivity ρ of the piezoelectric composition of Example 1 after the polarization treatment was 1×10 ¹² Ω·cm or more. Also in Examples 2 to 28 described later, the electrical resistivity ρ of the piezoelectric composition after the polarization treatment was 1×10 ¹² Ω·cm or more.

The piezoelectric composition of Example 1 was obtained by the above method. As a result of an analysis based on a fluorescent X-ray analysis method, the molar ratio of Bi, Fe, Ba and Ti in the piezoelectric composition was in agreement with the molar ratio of Bi, Fe, Ba and Ti in the above chemical formula A1. The values of x and y in the chemical formula A1 agreed with the values shown in Table 1 below. The mass ratio α of Ag in the piezoelectric composition was in agreement with the values shown in Table 1 below. The X-ray diffraction pattern confirmed that the piezoelectric composition had a perovskite structure.

The piezoelectric constant d ₃₃ (unit: pC/N) of the piezoelectric composition of Example 1 was measured using a d ₃₃ meter. The d ₃₃ meter is a device for measuring d ₃₃ by the Berlin coat method based on JIS (Japan Industrial Standards) R 1696. In the Berlin coat method, d ₃₃ is measured by utilizing the positive piezoelectric effect when vibration is applied to the piezoelectric composition. Therefore, in the Berlin coat method, unlike the measuring method using the piezoelectric inverse effect when an electric field is applied to the piezoelectric composition, there is no influence of electrostriction and the original d ₃₃ of the piezoelectric composition can be obtained. The d ₃₃ of Example 1 was the value shown in Table 1 below.

(Examples 2 to 28)
The x, y and α of Examples 2 to 28 were adjusted to the values shown in Tables 1 to 3 below by weighing the starting materials.

In Examples 3 to 28, the oxide of the element D was further used as the starting material. The elements D of Examples 3 to 28 are shown in Tables 1 to 3 below. In each of Examples 3 to 28, 100×M _D /M _ABO3 was adjusted to a predetermined value by weighing the oxide of the element D. M _D is the sum of the mass of the elements D contained in the starting material. In the following, the 100 × _M D _{/ M ABO3,} is denoted as beta. Β of each of Examples 3 to 28 is shown in Tables 1 to 3 below. Since element D was not used in Example 2, β in Example 2 was zero.

The piezoelectric compositions of Examples 2 to 28 were produced in the same manner as in Example 1 except for the above matters.

The piezoelectric compositions of Examples 2 to 28 were analyzed in the same manner as in Example 1. In any of Examples 2 to 28, the molar ratio of Bi, Fe, Ba and Ti in the piezoelectric composition was in agreement with the molar ratio of Bi, Fe, Ba and Ti in the chemical formula A1. In any of Examples 2 to 28, the values of x and y in the chemical formula A1 corresponded to the values shown in Tables 1 to 3 below. In any of Examples 2 to 28, the mass ratio α of Ag in the piezoelectric composition was in agreement with the values shown in Tables 1 to 3 below. In any of Examples 2 to 28, the mass ratio β of the element D in the piezoelectric composition was in agreement with the values shown in Tables 1 to 3 below. In each of Examples 2 to 28, it was confirmed that the piezoelectric composition had a perovskite structure.

The electrical resistivity ρ of each of the piezoelectric compositions of Examples 2 to 28 was measured in the same manner as in Example 1. Ρ before the polarization treatment of each of Examples 2 to 28 is shown in Tables 1 to 3. In the same manner as in Example 1, the piezoelectric constant d ₃₃ of each of the piezoelectric compositions of Examples 2 to 28 was measured. The d ₃₃ of each of Examples 2 to 28 is shown in Tables 1 to 3 below.

(Comparative Examples 1 to 8)
In any of Comparative Examples 1 to 8, Ag was not used as a starting material. In the weighing of the starting materials in each of Comparative Examples 1 to 8, x, y and β were adjusted to the values shown in Table 4 below. Since the oxide of the element D was not used in Comparative Example 1, β in Comparative Example 1 was zero.

Piezoelectric compositions of Comparative Examples 1 to 8 were produced in the same manner as in Example 1 except for the above matters.

The piezoelectric compositions of Comparative Examples 1 to 8 were analyzed in the same manner as in Example 1. In any of Comparative Examples 1 to 8, the molar ratio of Bi, Fe, Ba and Ti in the piezoelectric composition was in agreement with the molar ratio of Bi, Fe, Ba and Ti in the chemical formula A1. In each of Comparative Examples 1 to 8, the values of x and y in the chemical formula A1 matched the values shown in Table 4 below. In each of Comparative Examples 1 to 8, the mass ratio α of Ag in the piezoelectric composition was zero. In all cases of Comparative Examples 1 to 8, the mass ratio β of the element D in the piezoelectric composition was in agreement with the values shown in Table 4 below. In each of Comparative Examples 1 to 8, it was confirmed that the piezoelectric composition had a perovskite structure.

The electrical resistivity ρ of each of the piezoelectric compositions of Comparative Examples 1 to 8 was measured in the same manner as in Example 1. Table 4 shows ρ before the polarization treatment in each of Comparative Examples 1 to 8. The piezoelectric constant d ₃₃ of each of the piezoelectric compositions of Comparative Examples 1 to 8 was measured by the same method as in Example 1. D ₃₃ of each of Comparative Examples 1 to 8 is shown in Table 4 below.

A, B, C and D described in the judgment columns of Tables 1 to 4 below are defined as follows. A means that ρ is 1.0×10 ¹² Ω·cm or more (1E+ ¹² Ω·cm or more), and d ₃₃ is 160 pC/N or more. B means that ρ is 1.0×10 ¹² Ω·cm or more and d ₃₃ is 150 pC/N or more and less than 160 pC/N. C means that ρ is 1.0×10 ¹² Ω·cm or more and d ₃₃ is 140 pC/N or more and less than 150 pC/N. D means that ρ is less than 1.0×10 ¹² Ω·cm and d ₃₃ is less than 140 pC/N.

The piezoelectric composition according to the present invention is used, for example, in a piezoelectric actuator.

2... Substrate, 4... First electrode, 6... Piezoelectric substance (piezoelectric composition), 8... Second electrode, uc... Unit cell of perovskite structure.

Claims (6)

An oxide containing bismuth, barium, iron, and titanium; and silver,
The oxide has a perovskite structure,
The mass of the oxide is denoted _MABO3 ,
The mass of the silver is expressed as M _AG ,
100×M _AG /M _ABO3 is 0.01 or more and 10.00 or less,
Piezoelectric composition. Further containing at least one element D selected from the group consisting of vanadium, niobium, tantalum, molybdenum, tungsten and manganese,
The piezoelectric composition according to claim 1. As element D, at least niobium is further included,
The piezoelectric composition according to claim 1. The total value of the mass of the element D is represented as M _D,
100×M _D /M _ABO3 is 0.00 or more and 5.00 or less,
The piezoelectric composition according to claim 2. At least a portion of the oxide _is represented as _{x [Bi m FeO 3] -y} [Ba n TiO 3],
x is 0.6 or more and 0.8 or less,
y is 0.2 or more and 0.4 or less,
x+y is 1, and
m is 0.96 or more and 1.06 or less,
n is 0.96 or more and 1.06 or less,
The piezoelectric composition according to claim 1. A piezoelectric composition according to claim 1.
Piezoelectric element.